Interannual succession of phytoplankton community in a canyon-shaped drinking water reservoir during the initial impoundment period: Taxonomic versus functional groups

•The changes of phytoplankton and water quality in a reservoir were investigated.•The succession of phytoplankton was revealed using taxonomic/functional groups.•The high RWCS and WT were important reasons for the occurrence of algal blooms.•WT, RWCS, Zmix and pH were key factors affecting phytoplankton succession. During the initial impoundment period of a canyon-shaped reservoir, the water body fluctuated violently regarding water level, hydrological condition, and thermal stratification. These variations may alter the structure of phytoplankton community, resulting in algal blooms and seriously threatening the ecological security of the reservoir. It is of great significance to understand the continuous changes of phytoplankton in the initial impoundment period for the protection of reservoir water quality. Therefore, a two-year in-situ monitoring study was conducted on water quality and phytoplankton in a representative canyon-shaped reservoir named Sanhekou and the interannual changes of phytoplankton community and its response to environmental changes during the initial impoundment period were discussed at taxonomic versus functional classification levels. The results showed that the total nitrogen and permanganate index levels were relatively high in the first year due to rapid water storage and heavy rainfall input, and the more stable hydrological conditions in the second year promoted the increase of algae density and the transformation of community, and the proportion of cyanobacteria increased significantly. The succession order of phytoplankton in the first year of the initial impoundment period was Chlorophyta-Bacillariophyta-Chlorophyta, or J/F/X1-P/MP/W1-A/X1/MP, respectively. And the succession order in the second year was Cyanobacteria/Chlorophyta-Bacillariophyta-Chlorophyta, or LM/G/P-P/A/X1-X1/J/G. Water temperature, relative water column stability, mixing depth, and pH were crucial factors affecting phytoplankton community succession. This study revealed the interannual succession law and driving factors of phytoplankton in the initial impoundment period and provided an important reference for the operation management and ecological protection of canyon-shaped reservoirs. [Display omitted]